Conventionally, power supply to the central processing unit (CPU) and memory inside a server apparatus is implemented by supplying electric power generated from a power supply generation circuit in the same printed circuit board to electronic components including the CPU and memory using copper foil on the printed circuit board.
However, with demands for higher speed of CPUs and higher density, increase in current consumption and increase in power supply types are in demand. With the increase in power supply types, the number of power supply generation circuits is steadily increasing. Now that many power supply generation circuits are installed, installing power supply generation circuits and other electronic components on the same printed circuit board has reached a limit.
There is a power supply scheme that divides a board into a load board including electronic components serving as loads and a power supply board including power supply generation circuits for power supply and couples the load board and the power supply board to each other by bus bars.
Specifically, a bus bar for power feeding is brought into contact and fixed with a screw to a pad for supplying electric power generated by a direct current (DC)/DC converter disposed on the power supply board, and a bus bar for GND is brought into contact and fixed with a screw to a pad connecting to the ground (hereinafter abbreviated as GND). The bus bar for power feeding and the bus bar for GND are reinforced by fittings for preventing displacement and fixed to each other. The bus bar for power feeding and the bus bar for GND are brought into contact with the pads disposed on the load board and fixed with screws. Two clamps fixed to bus bars connecting to loads are inserted into the bus bar for power feeding and the bus bar for GND. The structure that couples the load board and the power supply board to each other with bus bars is thus completed. In this case, current flows from the bus bar for power feeding to the bus bar connecting to loads via the clamp to supply power to the load board. Current output from the loads then flows from the bus bar connecting to the loads to the bus bar for GND via the clamp and flows to the GND.
There is a conventional technique for supplying power from the power supply board to the load board, in which power is supplied through a power supply block disposed between a printed circuit board populated with semiconductor devices and a power supply bar extending from the back surface of the printed circuit board.
There is another conventional technique for keeping the space between boards by inserting a metal spacer between printed circuit boards and fixing the spacer with screws. In yet another conventional technique, a block with low-melting metal surrounded with an insulator is inserted between a semiconductor board and a mount board, and the boards are joined to each other by melting the low-melting metal. Conventional examples are described in Japanese Laid-open Patent Publication No. 63-152196, Japanese Laid-open Patent Publication No. 2001-156221, and Japanese Laid-open Patent Publication No. 2000-59000.
Unfortunately, when the power supply board is connected with the power feed board by bus bars, disposing the bus bars at the ends of the boards and fixing the C-shaped bus bars with screws increase the length of the power feed path and increase the resistance value of the power feeding conductor. It is therefore difficult to conduct appropriate power feeding due to a voltage drop and heat generation when large current is supplied.
Moreover, since the power feed path is long and the distance between the bus bar for power feeding and the bus bar for GND is wide, a large inductance component is produced on the power feed path. When the resistance and the inductance are large, the impedance of the power feed path is high. The amount of fluctuation of voltage supplied to the load increases in proportion to the amount of fluctuation of current and the impedance. Since the voltage fluctuation causes power supply noise, the greater impedance increases the noise at the load end. While the operating voltage of electronic components is decreasing year by year, the effect of power supply noise on the operation of electronic components is a serious problem, and reducing power supply noise is desired. A possible method for suppressing voltage fluctuation is to mount a large amount of capacitors. This method, however, increases the number of components and makes it difficult to reduce space and costs.